MYCHARGEMAN Forum

Temperature sensing is one of the most common applications used for specialty modules. There are quite a few different ways to measure the temperature though. We can put the methods into two different groups, contact and non-contact.

Non-contact temperature sensing is generally done with infrared light.

Since that is not typical used for logging or as an input to our systems, we'll focus on contact methods.

In our types of applications we're likely to come across three different contact temperature sensing methods. They are:

     1- Thermocouple

     2- RTD (Resistance Temperature Detector)

     3- Thermistor

Of the three different methods, thermocouple probably has the largest base out there. RTD comes in second place and thermistor follows in the back.

It's important to note that there are differences between them. The thermocouple, for example, works based upon a change in voltage. The RTD and thermistor have a different operating principle. They each work based on a change in resistance. Because of this fundamental operating principle difference, they are each best used in particular sensing applications. We'll learn more about each in the future.

The most important thing for us at this stage of understanding is how to go about choosing a sensor type. Some of the most important things to consider in your application are:

     1- Accuracy. You obviously need to sense temperature. How accurately do you need to sense that temperature? In other words, you need to know that the temperature is, for example, 125F +/- what?

     2- Resolution. What is the smallest unit that you need to know the temperature changed by? For example, you need to know the temperature is 125.001F would be a higher resolution than say 125.01F

     3- Repeatability. In simple terms, if you made the same measurement ten times (for example) the reading would be the same exact thing. In reality it will most likely deviate from reading to reading. The repeatability will determine that deviation specification.

     4- Temperature Range. The reality of the various technologies is that they don't all measure in the same temperature range. Be sure the product you use can take temperature readings in the particular range that you are measuring.

     5- Price. Self explanatory, don't you think?

Next time we'll start going through the operating principles of each technology so you can see why one way is better than another for your particular application.

eliskasim